The present invention relates to valves in general, and more particularly to a self-closing valve.
There are already known various constructions of self-closing valves of the type here under consideration. Typically, a self-closing valve of this type comprises a valve housing bounding an internal space and an inlet and an outlet communicating with the internal space and having a valve seat situated between the inlet and the outlet. A valve piston is received in the internal space for movement between a closing position in which it cooperates with the valve seat to interrupt communication between the inlet and the outlet and an open position in which it is spaced from the valve seat to establish such communication for enabling a fluid medium to flow from the inlet to the outlet. The valve piston delimits a relief chamber in the internal space. Such self-closing valves, which are being used, for instance, as flushing valves for toilets, shower fittings and the like, and which thus find a particularly useful application in the area of sanitary fittings, usually include a piston seal mounted on the valve piston for movement therewith and contacting the valve housing in a low-friction manner to separate the relief chamber from the inlet. The piston seal is often constituted by an annular collar or lip-type seal which includes a sealing lip that elastically contacts the inner surface of the circumferential wall section of the housing that bounds the relief chamber with a slight pretension and is guided on this inner surface.
Now, it cannot always be prevented with the required degree of assurance that, due to not entirely proper assembly or installation of the valve, contaminant particles, such as fine brass chips or the like, could reach or be present in the relief chamber. These contaminant particles, or at least most of them, rest on a downwardly disposed region of the inner surface of the wall which bounds the relief chamber. This is especially disadvantageous when the self-closing valve is installed in a horizontal position, since then the affected inner surface region is that of the circumferential wall section and thus such deposited contaminant particles can be transported by the relative movement of the valve piston in the housing, into the sealing region of the piston seal and cause the development of leakage currents thereat. These leakage currents then, in turn, negatively affect the flow balance of the relief chamber. This negative effect is especially detrimental in self-closing valve fittings in which an extended running time of a predetermined duration is customarily provided after the actuation impulse, in that it could result in deviations from the predetermined running time, or it could even bring about faulty functioning of the valve. However, similar problems could also be encountered even when the self-closing valve fitting is installed in a vertical position, especially when the closing direction of the piston valve extends in the downward direction. An attempt to avoid this problem by the provision of a second piston lip seal which would be effective for sealing in a direction opposite to that of the aforementioned piston seal appears to be disadvantageous. Besides the additional expense and space requirement, the second piston seal would increase the friction in a very undesirable manner. In any event, the contaminant particles would remain in the relief chamber and this could eventually result in the formation of ridges due to the frequent piston movements.